Keywords: maize, ecology, grain yield

Maize (Zea mays L.) is the third most important cereal crop in the world after wheat and rice and the most important cereal in Nigeria in terms of production and consumption. Maize is a renowned field crop in all the agro-ecological zones of West and Central Africa (WCA).¹ During the last two decades, production of maize have not coped with population growth due to several reasons includes low soil fertility which is the principal factor, little or no use of improved seed, herbicides, fertilizers, inad­equate plant density, weed infestation, poor tillage practices, labour shortages, increased levels of biotic and abiotic constraints, and high costs of inputs are some of the constraints associated with maize production.²

Maize is usually considered to have a high soil fertility requirement to achieve optimal yields^3,4 and thus large quantities of N is required. Nitrogen being the most yield limiting nutrient, its stress reduces grain yield by delaying plant growth and development.⁵ Maize is a nitro-positive and needs ample quantity of nitrogen for its better production.⁶ However, production is still seriously constrained by low soil fertility especially Nitrogen. Efforts aimed at obtaining high yield of maize would necessitate the augmentation of the nutrient status of the soil through a suitable application technique when it is most efficient and effectively utilized to meet the crop’s requirements for optimum productivity and maintain soil fertility. These studies were carried out to evaluate the effect of split N fertilizer application on growth and yield of extra early maize varieties.

The experiment was conducted during late season of 2014 planting season in Ibadan (forest-savanna transition) and Mokwa (southern guinea savanna) zones. Land preparation was done mechanically first and second ploughs, harrowed and marked with mechanical marker of 0.75m inter-row spacing. A factorial experiment fitted into randomized complete block design was used for both locations. The treatment were 5 varieties x 8 fertilizer rates making 40 treatment combinations replicated four times; three row planting of 5m long with inter-row spacing of 0.75mx0.25m intra-row spacing. The plot size was 5m x 2.25m with total experimental area of 90mx27.5m (2475m²). Basal application of P and K at rates equivalent to 30 kg P₂O₅ and K₂O ha^-1 respectively were made at time of first N application.

The following parameters were collected plant height, number of leaves, leaf area, stem girth, cob yield (t ha^-1), 1000 seed weight (g) and grain yield (t ha^-1). Growth parameters were taken at 4 and 8 weeks after sowing (WAS). 

Grain yield per heactare (t ha^-1):

Grain yield was estimated using the formula⁷ $\frac{\text{Field Weight }\left(\text{kg}/\text{plot}\right)\text{ x }\left(100-\text{GMC}\right)\text{ x }80/100}{85}\times \frac{10,000}{0.25\text{ x }0.75\text{x }21}$

Where:

Fw =field weight of ears at harvest

Gmc=grain moisture content (%)

0.8=shelling coefficient of maize (100^-15)= 15% moisture in grain at dry state 10,000m² = harvested area conversion into standard unit (ha)

The planting materials used were five cultivated extra early maize varieties comprising of striga tolerant maize varieties obtained from International Institute of Tropical Agriculture, Ibadan, (IITA). Data collected was subjected to analysis of variance (ANOVA) procedures according to the methods described. Treatment means were separated using the Duncan Multiple Range Test (DMRT) at 5% level of probability.⁸

Pre-cropping soil physiochemical properties analysis; the result showed that the soil used for field trials for both agro-ecology is sandy soil in texture, medium to slightly acidic soil, low in total Nitrogen (N), medium in available phosphorus (P). As result of its low essential macronutrients the soil can be regarded as a poor soil for maize production. The pH of 5.7 and 6.0 was moderate for maize production (Table 1). Very low in total Nitrogen (N of 0.09, 0.04kg^-1 of soil is less than the critical level of 1.5kg^-1, while the available phosphorus (P) of 8.7, 10.3mgkg^-1 exceeds the critical level of 8.10mgkg^-1. The pH of 6.0 was moderate for maize production (Table 1).

The data presented in Table 2, showed that maize varieties respond differently to Nitrogen fertilizer rates applied for both locations. Split N application rates greatly enhanced the performance of extra-early maize varieties in the various growth parameters measured. Application of nitrogen fertilizer produced significantly higher number of leaves, taller plants height, wider leaf area and thicker stem girth when compared with 0 kg N/ha. Application of 120kgN/ha split (60:60) applied at 2 and 4 WAS produced the highest number of leaves and widest leaf area when compared to other treatments in both locations. The tallest plant height and thickest stem girth was produced with the application rate of 90kgN/ha split (60:30) applied at 2 and 4 WAS. This result is an indication that higher levels of nitrogen fertilizer promote the vegetative growth in maize and its deficiency reduces the vegetative growth of maize. This agrees with Onasanya et al.,⁹ who reported higher application rate of 120 kgN/ha to produced the highest number of leaves. Also, Roth et al.,¹⁰ Paradkar et al., ¹¹ reported that higher nitrogen rate promotes vegetative growth in maize. Similar results that plant height increases with increasing levels of fertilizers were reported.^12–14 But these results are contrary to those of Jones¹⁵ who reported that time of application of N had no significant effect on maize plant characters. The least value for leaf area, number of leaves, plant height and stem girth was recorded in the control plot with 0kgN/ha. This result agrees with Tweneboah¹⁶ who earlier established that nitrogen deficiency retarded growth of maize and resulted into stunted growth and poor root development. For maize varieties, the highest plant height, widest leaf area and the thickest stem girth recorded for variety 2013 TZEE-W DT STR at 8 WAS could be attributed to their genetic make-up. It was also reported by Msarmo et al.,¹⁷ that cultivars grown under the same conditions may have differences in their performance based on the genetic characteristics. 

Amendment of soil by nitrogen fertilizer, irrespective of rates or period of application produced significantly better yield than 0kgN/ha. The data presented in Table 3, showed higher number of cobs at 60kgN/ha single applied (55.20 x 10³ and 51.60 x 10³) in both Mokwa and Ibadan respectively, while the lowest number of cobs produced was in the control plot (28.13 x 10³ and 29.2 x 10³) for both locations respectively. This result indicate that increase in N application do not show increase in number of cobs produced and environment did not have any effect on number of cobs produced in both locations, though mokwa agroecology brought about higher number in cob produced. The higher number of cobs experienced with N fertilizer application over the control may be due to the availability of Nitrogen nutrients throughout the growing season which is essential for optimum maize growth. This finding agrees with the earlier report^18,19 that the number of cobs produced by maize did not increase with the increase in nitrogen rates. Maize cob yield was greatly enhanced by varietal differences and split N application rates. Variety 2013 TZEE-W DT STR produced the best cob yield (3.33, 3.15 t ha^-1) for both mokwa and Ibadan.

Varieties had no significant (p>0.05) effect on grain moisture content among the maize varieties at both locations. TZEE-Y Pop C₄ had the highest grain moisture of (13.99 %) while the least grain moisture content was produced in 2013 TZEE-Y DT STR. Split N application rates showed significant effect on maize grain moisture content at Mokwa. The 90 kg N/ha split (60:30) applied at 2 and 4 weeks after sowing produced the highest cob yield (3.91 and 3.73 t ha^-1), grain yield (2.99 and 2.80 t ha^-1) and 1000 grain weight (432.2 and 414.9 g) in both Mokwa and Ibadan respectively. The least cob yield, grain yield and 1000 grain weight was recorded in the control plot with 0 kg N/ha in both locations. Cob yield of extra early maize was increased linearly with increase in N rates up to 90 kg N/ha. Split N application rate enhanced grain yield produced by extra early maize. This result agrees with¹⁸ that grain yield increased with increasing nitrogen rates. Similar, findings was reported that found that yield and yield component of maize were increase by increasing the rate of nitrogen application rates. Increase in maize grain yield with an increase in the rates of nitrogen was also reported,^20–23 in their investigations on nitrogen levels and maize grain yield.

For 1000 grain weight, the data in Table 3 reveals that the treatments were significantly different from one another. The different rates of nitrogen fertilizer and time of application influenced the size of maize seed produced. All the treatments where N was applied resulted in higher 1000 grain weight compared with the control. Varietal difference had no significant (p<0.05) effect on 1000 grain weight produced by the extra early maize materials. The 1000 grain weight produced was comparable for both agro-ecologies. 1000 grain weight were increased as N application rate increases up till 90 kg N/ha split (60:30) applied at 2 and 4 weeks after sowing and started decreased at 120 kgN/ha split (30:30:30) applied (Table 4).

The maize variety 2013 TZEE-WDT STR in both locations had higher number of leaves, plant height, cob dry yield, and grain yield at Mokwa and Ibadan respectively. Split N fertilizer application of 90kgN/ha at 2 and 4 WAS produce significantly higher 1000 grain weight, cob yield and grain yield at Mokwa and Ibadan respectively.

The control produced significantly reduced cob yield and grain yield in both locations compared to the rest treatments, therefore growing extra early maize without adding supplement of N fertilizer should be discouraged. The 2013 TZEE-WDT STR is the best variety in terms of growth and yield of maize at the two locations. Mokwa (9o18’N, 5o4’E) representing Southern Guinea Savanna showed to be a favourable environment to produce higher yield of maize using extra early maize varieties. Application of N in two split doses at (2 and 4 WAS) as 60:30kgN/ha on extra-early maize is recommended for achieving optimum grain yield in both locations.

None.

None.

The author declares there is no conflicts of interest.

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